The development of recombinant progency from crosses between Hordeum vulgare L. and H. bulbosum L.
Abstract
Crosses between Hordeum vulgare L. (cultivated barley) and H. bulbosum L. (bulbous barley grass) have been carried out for several decades to introgress desirable genes from the wild species into cultivated barley, but these projects have met with little success. Since H. bulbosum is considered to be the most closely related species to H. vulgare it was hypothesized in this thesis that interspecific genetic recombination is prevented by pre- or post-fertilization barriers. A series of investigations using H. vulgare x H. bulbosum hybrids was initiated to assess:
1 environmental effects on chromosome pairing by growing hybrids at two different temperatures and analyzing pollen mother cells at metaphase I;
2 crossing-over between homoeologous chromosomes at meiosis. This was carried out by producing diploid hybrids from crosses between a H. vulgare paracentric inversion stock and H. bulbosum. Pollen mother cells were analyzed at first and second anaphases, and anomalies (bridges and fragments) were related to frequencies of crossovers;
3 chromosome instability and elimination associated with particular parental combinations. 'VVB' hybrids had never been directly produced from crosses between H. vulgare (4x) and H. bulbosum (2x), so hybridizations were carried out at a temperature less than 17°C using genotypes known to promote chromosome retention;
4 production of progeny from crosses involving H. vulgare and partially fertile triploid hybrids ('VBB') of H. vulgare (2x) x H. bulbosum (4x). Any viable plants obtained were to be screened cytologically, pathologically and morphologically;
5 the use of anther culture to avoid certation effects after hybridizing H. vulgare with pollen from hybrids. Anthers from a range of diploid, triploid and tetraploid hybrids were cold pretreated and cultured according to protocols developed specifically for barley.
It was concluded from the investigations that optimum environmental conditions may be determined for individual hybrids to promote chromosome pairing but that crossing-over between paired homoeologues is greatly reduced compared with intraspecific H. vulgare hybrids. Novel triploid 'VVB' hybrids were obtained and certain genotypic combinations proved to be relatively stable. However, because of a lack of allosyndesis their use for gene introgression will be limited. Progeny from crosses between H. vulgare and partially male fertile 'VBB' hybrids included the first reported monosomic substitutions of H. bulbosum chromosomes into H. vulgare. These will be valuable for transferring genes from H. bulbosum to H. vulgare and locating them on particular chromosomes. Finally, although only few green regenerants were obtained from culture of anthers from hybrids one of these was characterized as a chromosomally modified diploid 'VB' hybrid with partial anther dehiscence. Progeny from crosses between this plant and H. vulgare demonstrated that chromosome additions and substitutions can be developed.
